Hello AT and welcome to the forum.
While replacing the hinges should be simple(ish) it might be a challenge to find the right replacements.
First thing is to understand exactly what you van is!
1 - If it’s like mine (take a look at the ‘Show Us Yours’ section under my username) then it’s a Toyota factory-made pop-top and I’ve no idea where to get roof parts. If so, I’m surprised these are rusty as they are very well made and well protected. Here, your best bet might be to repair what you have or get a local company to make some replacements. If you can work out the dimension or if there’s any build numbers on them then these might help a lot. The Toyota Electronic Parts Catalogue (EPC, see below) does not cover the pop-top fitted to the factory-build vans. but it's great for the rest of the van.
2 - If it’s a non-Toyota conversion then your best bet (I think) is to approach the company that did the conversion. Sometimes this is fairly obvious as the van will have a maker’s plate or paperwork or sticker. Reimo is a common converter and Danbury’s also another big name. Point is if you can track down the company and they are still in business then you can start by asking if they still stock parts or have something equivalent. I think this will be the best approach. The company might also recommend a garage, workshop or converter who can do the swap if you can’t do it yourself. I can’t see replacing the hinges will be that difficult but it might need a few people to help and getting everything aligned could take some expertise. Plus you need to be extra careful to not make things worse or damage what you have for the time being.
Above I mentioned the EPC. See this recent post, here:
https://hiace-super-custom.forumotion.com/t4468-part-numbers#24952for ways to dig into this and other resources and sites that might be useful. The starting point is to decode the numbers etc on the van’s
build plate, which is under the passenger seat.
Next, once you have made a (this) post similar threads appear below it. These can be helpful, or not. The forum itself is not that easy to search. Sometimes it's easier to search in google but add the forum name to the term.
Also, once a little time has passed, you’ll be able to post pictures that might be helpful. The image hosting method is a bit old skool.
Good luck and do report back!!